This invention relates to an explosive cutting device for cutting chain links, rods, bars, cables, lines, and the like, particularly disposed beneath the surface of water, at a a preselected time or distance from the surface of the water.
It is often desirable to temporarily anchor floating vessels such as drilling ships, floating drilling platforms, buoys and the like in great depths of water. Such vessels are held stationary on the surface of the water by a length of anchor chain, cable or line attached to an anchoring means. In offshore operations it is desirable to have a reliable, quickly releasable anchor system. Typical unpredictable conditions experienced by offshore drilling ships, floating drilling platforms, and the like, which require the drilling ship or floating drilling platform to be moved as quickly as possible from anchorage, include adverse weather conditions, blowouts, drifting icebergs or any other emergency situations.
In the past, offshore drilling ship and floating drilling platform anchor chain release mechanisms have been cumbersome to install, expensive to purchase and require periodic maintenance to insure reliability. For example, a prior art hydraulic anchor chain release mechanism which is installed between the anchor on the ocean floor and the anchor chain is approximately 103 inches in length, 24 inches in diameter, and weighs 4,400 pounds on land.
Another prior art explosive cutting device for use on anchor chains, which merely comprised two shaped charges that were installed on an anchor chain link and detonated by explosive detonating cord, was found to be unsatisfactory in service since it required the shaped charges to extend one foot or more on either side of the anchor chain link to insure the severing of the anchor chain link upon detonation.
In contrast to the prior art devices, the present invention provides an explosively actuated anchor chain cutting device which comprises an upper member and a lower member, each having linear shaped explosive charge contained therein, the members being held about an anchor chain link by any suitable fastening means and a means for detonating the explosive charge in the upper and lower member respectively. When compared to the prior art anchor chain release mechanisms or cutters, the present invention is relatively inexpensive, can be easily installed and manipulated by a technician, and requires a minimum of periodic maintenance. The present invention also offers the advantage of severing relatively large diameter anchor chain links using a minimum amount of linear shaped explosive charge since the linear shaped explosive charge in each member of the explosive cutting device is simultaneously detonated. This provides a jet of hot gases and particulate materials which cut from both sides of the anchor chain link simultaneously. In conjunction with the simultaneous detonation of the linear shaped explosive charges in the upper and lower members of the cutting device, the present invention further includes anti-jet distortion members which allow the jet and particulate material emanating from each linear shaped explosive charge to remain undistorted by the surrounding environment thereby insuring complete severing of the anchor chain link.